Java Reference
In-Depth Information
8.4.2. Method Signature
Two methods have the
same signature
if they have the same name and argument types.
Two method or constructor declarations
M
and
N
have the
same argument types
if all of the
following conditions hold:
• They have the same number of formal parameters (possibly zero)
• They have the same number of type parameters (possibly zero)
• Let
A
1
, ...,
A
n
be the type parameters of
M
and let
B
1
, ...,
B
n
be the type parameters
of
N
. After renaming each occurrence of a
B
i
in
N
's type to
A
i
, the bounds of cor-
responding type variables are the same, and the formal parameter types of
M
and
N
are the same.
The signature of a method
m
1
is a
subsignature
of the signature of a method
m
2
if either:
•
m
2
has the same signature as
m
1
, or
Two method signatures
m
1
and
m
2
are
override-equivalent
iff either
m
1
is a subsignature of
m
2
or
m
2
is a subsignature of
m
1
.
It is a compile-time error to declare two methods with override-equivalent signatures in a
class.
Example 8.4.2-1. Override-Equivalent Signatures
class Point {
int x, y;
abstract void move(int dx, int dy);
void move(int dx, int dy) { x += dx; y += dy; }
}
This program causes a compile-time error because it declares two
move
methods with
the same (and hence, override-equivalent) signature. This is an error even though one
of the declarations is
abstract
.
The notion of subsignature is designed to express a relationship between two methods
whose signatures are not identical, but in which one may override the other. Spe-
cifically, it allows a method whose signature does not use generic types to override
any generified version of that method. This is important so that library designers may
